RESPONSE OF THE TOMATO PEROXIDASE GENE tpx1 TO BIOTIC LICITORS

WEVAR OLLER, A. L., AGOSTINI E., MILRAD DE FORCHETTI S. R., TIGIER H. A. Y MEDINA M. I.

Villa General Belgrano

Congreso; XIV Jornadas Científicas SBC; 2003

SBC

Peroxidases (Px) have been involved in several physiological and biochemical processes, such as abiotic and biotic stress responses and lignosuberization. This is a defense mechanism against pathogens that limits their spread at the infection site. In tomato, tpx1 gene encodes an isoperoxidase with a pI 9,6 which has been related to lignification. Furthermore, tpx1 expression is induced by salicylic acid that is an endogenuos elicitor for the activation of defense responses. To study the effect of biotic elicitation on tpx1 gene expression, we used tomato (Lycopersicon esculentum Mill.cv.Pera) hairy roots as a model system. We used chitosan as purified biotic elicitor (200 mg/l) and the specific phytopathogenic fungus Fusarium oxysporum f.sp.lycopersici as complex elicitor (105 y 106 conidia/ml). Soluble (SP) and ionically-bound to cell wall (IBP) proteins were extracted. Px activity was measured and isoenzymes were separated by IEF and cationic PAGE. Total RNA was isolated and transcript accumulation was tested by Northern blot. Px activity of tomato hairy roots treated with chitosan increased about 50 % at 2,5 h. post-elicitation. It was coincident with an increased intensity of the band with a pI 9,6 in the IEF and accumulation of tpx1 transcripts. In the SP fraction chitosan stimulated Px activity about 76 % without alteration of isoenzyme patterns or tpx1 transcription. Treatment with Fusarium conidia didn´t altere isoenzyme patterns or tpx1 transcription, but enhanced Px activity in the SP fraction with both concentrations, and in the IBP only with 105conidia/ml at 48 h. post-elicitation. In conclusion, tpx1 expression was induced by chitosano at 2,5 h., but not by Fusarium conidia at longer times.